Mounting of airscrew blades



May 6 1941-. r-'. M. THoMAs IMOUNTING 0F AIRSCREW BLADES Filed Noi. 7,1938 Patented May', 1941 MOUNTING or` Amsoanw ananas Frederick MetcalfThomas, Hatfield, England, as-

signor to The De Havilland Aircraft Company Limited, Hateld AerodrornefyHertfordshire,

England vAppunti@ November r, 193s, serai No. 239,386 y In Great BritainNovember 1l, 1937 l 5 claims` (cl, '11o-162).

This invention relates to airscrew blades and the mountingthereof,particularly such as are of variablev pitch. A n 'object of theinvention is to provide an improved insulation' for the blade mountingagainst attrition, vibration'or shock between the airscrew bladeandother parts transmitting load. A further object is toprovide aninsulation which may avoid thetransrnisbeing interposed between the boreand driving member a layer of insulating material. 'I'hus according toone aspect of the invention, there isV provided an airscrew withbladesof the kind having internal bores at the root ends forming ajournal for pitch changing rotationon a. spider or llike supportingbearing part, wherein a layer of vibration insulating material isinterposed between the surface of the yblades vinternal bore and thespider. According toa further feature of the invention, an airscrewblade for a variable pitch airscrew, which is adapted to be mounted forpitch changing rotation between internal and external bearings, has alayer of vibration insulating material 'both internally and externally.thereof interposed between the blade and both such bearing parts, thatis, between the blades bore andthe internal bearing on the spider, and

' the blade.

between the blades ange and the external retaining Aring or barrel.

v2in one application of the inventionvthe blades are of the ,metallickind, whilst-the vibration insulating material is preferably in thenatureof a reinforced synthetic resin, a rubber composition, a softmetallic alloy, or metal-containing composition. While theA inventionhas particular reference to blades of vvariable pitch airscrews ,mountedbetween internal and external bearings, It is also applicable to certainforms of xed'and adjustable pitch airscrews. In this case the in-lsulation would be provided between the external part of the blade andafretaining member, and between an internal bore of the blade andadrivbore adapted to form a journal for pitch changing rotation, andthere is moulded to the internal surface thereof, and also on the outersurface at the root end, a layer ork covering of suitable insulatingmaterial such as synthetic resin, the external layer serving to insulatea thrust bearing allowing pitch changing rotation and the internal layerinsulating a journal bearing.

The invention is illustrated in the accompanying drawing in which the:dgure is a diagrammatic cross section through the root end of anairscrew blade, showing its mounting ktothe airscrew hub through thrustand Journal bearings arranged externally and internally of the shank ofthe blade.

In the drawing the hub comprises a driving member=l splined upon theairscrew shaft Il, and supporting at its forward end the hydraulic jackmechanism diagrammatically shown at I2,

whose root or shank is shown in section at I3.

The shank is hllowed out at I4 to receive a.

spider or journal bearing I5 which extends radially from the hub I0, andserves for the transmission of power from the airscrew shaft II to Thespider I 5, from lthe point of view of` pitch changing rotation aboutthe longitudinal axis of the blade, may thus V`be considered as xed.Externally of the blade shank there is a thrust bearing comprising arelatively fixed race I6, rollers 'I1 and a race I8, the latter beingnon-- rotatably carried on theblade shank I3. The race I6 is carried inthe support, retaininglring, or barrel. I9 secured to the hub, wherebycentrifugal thrust loads in the blade are transmitted to the hub.

The insulating layer is diagrammatically indicated at 20, and as showncovers the whole surface of theinternal bore Il for somedistance fromthe root, and extends by a thin lm 22 to the external surface of theblade shank I3 and over the outer surface of the blades flange 2 I, as4shown at 23, where it is interposed between the race I8 and the bladeI3. Preferably the insulating material is of reinforced synthetic resinor a rubber composition,` and may be moulded in situ so as to` :coverthe entire root end as shown in the drawing. f

It will benotedjhat the internal insulating layer is interposed betweenthe blade I3 and spider journal I,and within the internal bore isrelatively thick, whilst adjacent the collar or flange 2l on the blade'externally thereof, the insulation is again thickened. It will beappreciated that the flange 2| serves as an abutment manner and pushedinto the bore of the blade,

the tapered part thereof serving to secure the insulation in position,Whilst the external partA 23 of the insulating'material may be made as asplit collarwhich can be slipped over the tip of the blade to the bladeshank and this coll-ar may be cemented or'otherwise ilxed in position.'I'he internal and external parts may be of the same 'or differentmaterial and the internal part may incorporate metal liners to act asbearing surfaces for the spider member.

. What I claim is:

1. vIn an airscrew, in combination, blades each f ormed with an internalbore at the root end, a hub including radial spider arms each receivedwithin such a bore to constitute internal radial bearing means,andincluding external bearing means\su rrounding each blade root andconcentric with the corresponding spider arm, .and a layer of syntheticresin'or the like, molded in synthetic resin or the like are formedintegrally,

n 2,240,873 transmitting the thrust loads in the blades to situ, andinterposed between and effecting a close bearing t between the bladeroot and each of the internal and external bearing means.

2. The combination according to claim 1, where -the external and theinternal layers of as one piece.

3. In an airscrew, in combination, a hub includingy radial spider arms,blades each formed with an internal bore at the root end, wherein isreceived a spider arm, a layer of synthetic resin or the like, molded insitu, and interposed between and centering the spider within the bore,to form .a close radial journal bearing for the root end of the bladeupon the hub, a retaining ring surrounding the root Iend of the bladeand secured upon the hub, a thrust bearing reacting between theretaining ring and the blade root, and a similar layer of syntheticresin or the like, molded in situ and similarly interposed between theblade root and the retaining ring.

4. The combination according to claim l, wherein the external andinternal layers of molded synthetic resin or the like are so disposed asto prevent any contact between the blade and the hub, or parts thereofor carried thereby.

5. .The combination according to claim l, wherein the two layers ofmolded synthetic resin, or the like, internally and externally of theblade root are formed integrally, as one piece, and are thickened inregions of maximum stress.

FREDERICK M THOMAS.

